Proces of making granular sodium bichromate.



' UNITED STATES PATENT OFFICE. nunonr' casranr, or unnnmonn, GERMANY, essmnon 'ro n. wnnnxmn' & 00., m. B. IL, or UEBDINGEN, aEnmANY.

PROCESS OF MAKING GRANULAB SODIUM BICHROMATE.

1 ,003,87 5. No Drawing.

' Specification of Letters Patent,

Patented Sept. 19, 1911.

To all whom it may com-em:

' fused lumps, 4th, powder, made from the fused lumps by grinding and screening. In either form it analyzes about ,67 to 68% of chromic acid (CrO while Na,,Cr,,O theoretically contains 76.3% CrO, so that in shipping the commercial products freight has to be aid on the water resent therein. Besides, t e crystals (Na r,O-,,2aq. with 67.1% (JrO are "cry hygroscopic, the fused lumps are unhandy on account of their size, and if broken up or ground to a powder,

, very annoying and harmful dust is formed,

not only during the rocess of grinding and screening, but also w ile the product is handled later on. I have discovered that none of these difliculties and annoyances is conwater containing salt granulated e. g. by

grinding and screenin The 'salt freed from its mother-lye b'y suction filters or centrifugals is gradually heated in a revolving steam-jacketed cylinder or in a vessel with a stirrer placed over a stove, until it reaches the melting point of crystallized bichromate of sodium, or to about 110 0., while a sufficient quantity of air is passed over the material to solidify the softening crystals or granulated particles before they cake, and in order to immediately take away the steam generated. The partly dried material soon commences to roll, as the small crystals or granulated particles readily give ofi the adering' moisture as well as the water of crystallization. The dehydration proceeds without any material change of the form of the crystals or of the granules and without any Application filed September 7, 1910. Serial no. 580,814.

formation of dust. Accordin to the percent-a e of chromic acid desire in the product, t e dehydration is either completed or interrupted after it has proceeded to the desired oint. In the first case a gradual rise of t e temperature to about 130 0. accelerates the process.

The product re resents a non-dustin vividly red, ranu ar and therefore han y bichromate 0 sodium, containing up to 75% chromic acid (l Ta,Cr,O contains 76.3% CrO theoretically) according to the degree of dehydration and the percentage of impurities in the starting material. It is less ygroscopic than the large crystals or the lum s of the trade.

T e process can be modified in the manner that a solution of bichromate of sodium is added to the material while being dried, gradually and in such quantities as will continuously dry on the-surface of the crystals or of the granules, until these have reached the :desired size or as long as no dust is formed b the friction of too large particles. The pro uct consists of spherical granules, free from dust, of a vivldly red color, a

handy form and with a high percentage of.

chromic acid.

It was not to be foreseen that a moist mass of small crystals or ranulated particles would yield a product with so desirable properties. It was on the contrary to be expected, that the mass would behave similarly as it does, if being dried without motion, viz., cake or fuse, and develop dust during the final stage of the drying as well as while being ground.

I cla1m 1. The process of makin granular sodium bichromate which consists 1n heating a mass of crystallized salt gradually to near its melting point during agitation and remov; ing the steam as it generates during said heatin step.

2. T e process of making granular sodium bichromate which consists in heating a mass of crystallized salt gradually to near its melting point during agitation and bringing a current of air into contact with said mass to remove the steam as it generates during said heating step.

3. The process of making granular sodium bichromate which consists in heating a mass melting point du ring agitation, adding such two subscribing witnesses. proportion of a solution of sodium biChI'O. mate as will dry onthe surface of the 5 granules formed, and removing the steam Witnesses:

as it generates during said heating step. HENRY QUADFLEG, In testimony whereof I have signed my WELIAM J. REUTERS.

of crystallized-salt gradually to near its name to this specification, in the presenceof RUDOLF CASPARI. 

